Do you tile walls or floor first?

Whilst you can tile either one first, popular opinion based on experience is that is is easier to tile the walls first and then the floor, if you are tiling both in a room. This ensures that you keep the floor tiles cleaner as you won't be doing so much work around them once they are installed.

Where do you start when tiling a floor?

Find the midpoint of each wall and snap chalk lines on the floor. The line crossing at the room's center are the starting point of the tile. Lay a row of tiles along a straightedge more than halfway across the room. For consistent joints, use tile spacers.